1. Field of the Invention
Embodiments of the present invention generally relate to managed pressure cementing.
2. Description of the Related Art
In wellbore construction and completion operations, a wellbore is formed to access hydrocarbon-bearing formations (e.g., crude oil and/or natural gas) by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on a surface platform or rig, and/or by a downhole motor mounted towards the lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore. An annulus is thus formed between the string of casing and the formation. The casing string is hung from the wellhead. A cementing operation is then conducted in order to fill the annulus with cement. The casing string is cemented into the wellbore by circulating cement into the annulus defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
Once the initial or surface casing has been cemented, the wellbore may be extended and another string of casing or liner may be cemented into the wellbore. This process may be repeated until the wellbore intersects the formation. Once the formation has been produced and depleted, cement plugs may be used to abandon the wellbore. If the wellbore is exploratory, tests may be performed and then the wellbore abandoned.
Not all wells that are drilled and casing strings cemented in place during the well operation are problematic. Conversely, primary cementing of problematic wells has historically been inefficient to unobtainable by manipulation of the traditional variables. What can be recorded today to effectively measure the success or failure of a primary cement job is not adequate for cementing problematic wells. Understanding the objectives of a primary cement job, being able to execute the primary cement job and adequately interpreting the results have ultimately been the criteria of a success or a failure. Whether success is a leak-off test, open-hole kick-off plug, isolation of a hydrocarbon bearing zone of interest, or a fresh water zone that must be hydraulically or mechanically isolated and protected, the tools and methods that operators and service companies employ today that can be controlled and monitored are not always enough to provide the expected nor the desired results.